User agent has managed by group. Naming your group on Title field.
on User Agent strings. Put your custom user agents here, one per line. For example. I'm creating a group of user agents for Firefox.
On the Sizes fields. Add the browser sizes that will apply to this user agent group. You may add more than one size.

So how the system use your custom user agent? While surfing sites, the
9Hits Viewer will take random one user agent from User Agent strings,
combined with one random size from your added Sizes. For example, the viewer may take from Firefox group (the example on above figure) an user agent:

From add/update website, go to the Platforms option. There are three types: Mobile, Desktop and Custom.

Mobile and Desktop is the build-in user agents (managed by the system). Custom is your own user agents. You may adjust the slider (adjust the usage rate of each type) to tell the viewer how it should use there types. Of course you can use combining there types or just one, or two of them. To use your custom, you have to set Custom rate greater than zero percent. And now, the list of your custom user agent would appear, just choose which group that you want to use. In the example bellow. I would like to use 30% mobile, 38% desktop user agent from the system, and 32% of my own Firefox user agents.